Answer:
The correct answer would be option C, 24
Explanation:
24 participants will be needed by psychologists at a minimum, to perform his experiments.
This is basically a statistical question in which the possible outcomes of the minimum number of people needed for the experiment is required.
So such questions can be solved by a simple method in which we take the number of techniques and multiply them with their descending number till 1. For example in this question, the number of techniques are 4. so it would be 4! which means we can take out the minimum number of participants by 4*3*2*1, which equals 24. So 24 is the answer.